1. Field of the Invention
The present invention relates to an ink jet recording method with which an image is recorded on a recording medium by discharging ink onto the recording medium.
2. Related Background Art
In the field of ink jet recording, there have conventionally been used blank inks including pigments to form, in particular on plain paper, black images excellent in printing density, printing quality, and fastness properties such as water fastness and light fastness. There have also conventionally been used ink sets that prevent blurs (hereinafter referred to as xe2x80x9cbleedingxe2x80x9d) that occur at boundaries between image areas printed with blank inks and their adjacent image areas printed with color inks or prevent irregular blurry white images (hereinafter referred to as xe2x80x9cwhite hazexe2x80x9d) that occurs in black image areas at boundaries with color image areas.
Representative techniques are disclosed in Japanese Patent Application Laid-Open No. 6-106841, Japanese Patent Application Laid-Open No. 9-11850. Japanese Patent Application Laid-Open No. 11-334101, Japanese Patent Application Laid-Open No. 11-343441, U.S. Pat. No. 5,428,383, U.S. Pat. No. 5,488,402, and U.S. Pat. No. 5,976,230. In these documents, bleeding is suppressed using an ink set that includes a black ink and color inks, with at least one of the color inks having mutual reactivity with the black ink and other color inks having non-reactivity with the black ink. There is also described an ink jet recording method using this ink set. In particular, there is disclosed a printing method (hereinafter referred to as xe2x80x9cunderprintingxe2x80x9d) with which a color ink having reactivity with the black ink is printed over an black ink print area to prevent bleeding at boundaries between print areas formed with the black ink and print areas formed with the color inks having non-reactivity with the black ink.
As a result of studies conducted by the inventors, however, it has been newly found that the underprinting described above has the following problems.
The first problem is that the aforementioned prior art documents do not specifically describe how to apply the color ink having mutual reactivity with the black ink to the black print area during the underprinting. Depending on the manner in which the color ink is applied, a sufficient effect of preventing bleeding cannot be obtained. In particular, although there is a description concerning the metal ion concentrations of the inks, it has been newly found that the metal ion concentrations are not the main factor for suppression of bleeding.
The second problem is that because only the color ink having reactivity with the black ink is applied (underprinted) in the black print area, the color phase direction in the black print area is shifted toward the color phase of the underprinted color ink. Further, if the underprinted color ink spreads outside the black print area, the spreading color ink causes a color change from the original color around the black print area. This problem becomes more serious if deviations in impingement position between black ink droplets and color ink droplets occur for some reason such as cock ring that is a phenomenon where a recording sheet is warped in a wave manner due to the adhesion of an ink on the recording sheet.
The present invention has been made in the light of the above-mentioned problems of the ink jet recording method utilizing the underprinting technique. The object of the present invention is to clearly define the conditions that should be satisfied when a reactive color ink having a mutual reactivity with a black ink is underprinted in a black ink print area, and to provide an ink jet recording method with which bleeding and white haze are suppressed.
The stated object is achieved by an ink jet recording method that uses an ink set including a black ink and a plurality of color inks, at least one of the plurality of color inks containing a metal ion and being a reactive color ink that exhibits mutual reactivity with the black ink, each color ink other than the at least one reactive color ink being a non-reactive color ink that exhibits non-reactivity with the black ink, the ink jet recording method including: a step for applying the at least one reactive color ink in an area in which the metal ion becomes effective at promoting a reaction between the black ink and the at least one reactive color ink, where the at least one reactive color ink is applied in the area so that a value at least equal to 0.01 is obtained from a calculation where (a metal ion concentration (% by weight) in the at least one reactive color ink applied in the area) is multiplied by (a print duty (%) of the at least one reactive color ink applied in the area).
The stated object is also achieved by an ink jet recording method that uses an ink set including a black ink and a plurality of color inks, at least one of the plurality of color inks containing a metal ion and being a reactive color ink that exhibits mutual reactivity with the black ink, each color ink other than the at least one reactive color ink being a non-reactive color ink that exhibits non-reactivity with the black ink, the ink jet recording method including: a step for applying the at least one reactive color ink in an area in which the metal ion becomes effective at promoting a reaction between the black ink and the at least one reactive color ink, where an application amount per unit area of the metal ion applied in the area is at least equal to 0.1 ng/mm2.
By regulating the metal ion concentration and print duty of the reactive ink underprinted in the black print area in the manner described above, it becomes possible to obtain an effect of preventing bleeding and white haze occurring at the boundary between the black print area and an adjacent print area formed with the non-reactive color ink.
Here, it is preferable that the total application amount of the at least one reactive color ink applied in the area is at least equal to 50% of a total application amount of each non-reactive color ink applied in the area.
Also, a print duty of the at least one reactive color ink applied in the area may be at least equal to 10%.
Further, the area includes a print area formed with the black ink and an area surrounding the print area, a distance between an edge of the print area and an outer edge of the surrounding area being up to four pixels. By doing so, even if the area in which the reactive color ink is applied is shifted from the black print area to some extent, it becomes possible to obtain the effect of preventing bleeding and white haze by underprinting the reactive color ink.
Further, the metal ion may be at least one polyvalent metal cation selected from a group consisting of Mg2+, Ca2+, Cu2+, Co2+, Ni2+, Fe2+, La3+, Nd3+, Y3+, and Al3+.
Further, each reactive color ink may contain metal salt whose amount is within a range of from 0.1 to 15% by weight based on a total weight of the reactive color ink.
Furthermore, the black ink may contain salt and uses a black pigment as a coloring material.
The stated object is further achieved by an ink jet recording method that uses an ink set including a black ink and a plurality of color inks, at least one of the plurality of color inks being a reactive color ink that exhibits mutual reactivity with the black ink, each color ink other than the at least one reactive color ink being a non-reactive color ink that exhibits non-reactivity with the black ink, where the plurality of color inks include specific color inks that have a relation where overlaying of the specific color inks produces a black color, and the specific color inks include at least one reactive color ink and are applied in an area including at least a print area formed with the black ink.
This ink jet recording method of the present invention makes it possible to suppress the change of black color tone in the black print area caused by the application of the reactive color ink.